article: After a quick breakfast, I went into the lecture  hall in a hurry. A famous teacher was speaking to the students. He was holding up a $100 bill. Then he said to over 300 students, " Who would like this $100 bill?" The students put up their hands at once. Then he said, "I am going to give this $100 bill to one of you, but first, let me do this." He made the bill into a ball. Then he said, "Who wants it now?" The hands went back into the air. "Well," he said, "What if I do this?" and he dropped it on the floor and stepped on it. He picked up the dirty bill and said, "Who still wants it?" Hands went back again into the air.
  "My friends," he said, "you have learned a valuable lesson today. No matter what I did to the $100 bill, you still want this bill. Many times in our life, we are dropped and stepped on. We feel as if we are worth nothing. But remember, no matter what has happened to you, you will never lose your value. You are always valuable to those people who love you. Your value doesn't come form what you do or whom you know, but who you are."
question: The lesson tells us a truth, that is  _  .
options: we should know what we do we should know whom we know we must know who we are how to use money